DES-mediated synthesis of ZnO nanostructures with exposed {0001} facets: photoluminescence and photocatalytic properties

Abstract

In this paper, deep eutectic solvents (DESs), namely choline chloride/ethylene glycol and choline chloride/citric acid, are employed as efficient templating agents for the controlled fabrication of zinc oxide nanostructures with unusual morphology such as petal-aggregated flower-like and cauliflower-like 3D hierarchical structures via a simple hydrothermal approach at 150 °C for 15 h. The obtained samples were characterized by XRD, TEM, SEM, UV-Vis diffuse reflectance spectroscopy and photoluminescence (PL) studies. The XRD analysis confirmed the presence of the hexagonal wurtzite structure of ZnO and the morphology results demonstrated the structure-directing effect of the deep eutectic solvents, which leads to exposure of the {0001} facet. The temperature-dependent growth behaviour of the nanoparticles directly indicated the formation of different shapes owing to the percentage difference in the exposed facet. The photoluminescence spectra showed that the prepared ZnO nanostructures exhibited strong green emission related to oxygen vacancies and defects. The synthesized flower-like ZnO nanostructure showed a higher photocatalytic degradation efficiency toward methyl orange as compared to commercial ZnO powders.